Field ion microscope investigations of adatom and dimer diffusion along Rh(100) step edges

Activation energies of surface diffusion for atoms and dimers migrating along straight edges of rectangular-shaped islands on Rh(100) were measured by held ion microscopy. Single atoms diffuse along the step with an activation energy of 0.58+/-0.02 eV. This value is comparable to that for self-diffusion on the channeled Rh(311) plane (0.54 eV), which has the same local atomic structure as the step. The activation energy is considerably smaller than that for self-diffusion on the Rh(100) terrace (0.83 eV). Dimers diffuse along the step with an activation energy of 0.80+/-0.02 eV. The energy barrier for an atom to move around the corner of an island is estimated from the onset temperature to be similar to 0.9 eV. The measured diffusion barriers are discussed in relation to island growth on fee metal surfaces.